Conventionally, as for the amount of refrigerant in a refrigerant circuit of an air conditioner, the air conditioner is operated under specific conditions in order to judge whether or not an adequate amount of refrigerant is charged which is in accordance with the size of the air conditioner, length of a communication pipe of the refrigerant circuit, and the like. In the operation of the air conditioner under such specific conditions, a judgment is made as to whether or not an adequate amount of refrigerant is charged by, for example, detecting the subcooling degree of the refrigerant condensed in a condenser while performing an operation in which control is carried out such that the superheating degree of the refrigerant evaporated in an evaporator reaches a predetermined value.
However, in such an operation, even it a predetermined superheating degree was attained, the pressure in each portion in the refrigerant circuit changes depending on factors such as the temperature of the indoor air that exchanges heat with the refrigerant in a utilization side heat exchanger, the temperature of the outdoor air as a heat source that exchanges heat with the refrigerant in a heat source side heat exchanger, and the like, which consequently changes the target value of the subcooling degree at the time of judging whether or not the amount of refrigerant is adequate. Consequently, it is difficult to improve the judgment accuracy at the time of judging whether or not the amount of refrigerant is adequate.
With respect to this problem, according to JP Pat. Appln. No. 2004-173839 below, the judgment accuracy for the amount of refrigerant charged in a refrigerant circuit is improved by performing a superheating degree control by a utilization side expansion mechanism and an evaporation pressure control by a compressor and detecting the subcooling degree of the refrigerant at the outlet of a heat source side heat exchanger.